Disclosed embodiments relate to additive manufacturing systems. In some embodiments, an additive manufacturing system includes a fixed build plate, and a build volume extends above the fixed build plate. A boundary of the build volume may be defined by a powder containing shroud that is vertically displaceable relative to the fixed build plate. A powder deposition system is configured to deposit a powder layer along an upper surface of the build volume and the powder deposition is vertically displaceable relative to the fixed build plate. An optics assembly configured to direct laser energy from one or more laser energy sources towards the build volume, and exposure of the powder layer to the laser energy melts at least a portion of the powder layer. In some embodiments, the build plate may be supported by support columns configured to maintain the build plate in a level orientation throughout a build process.
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1. An additive manufacturing system comprising:
a build plate vertically supported by two or more support columns, wherein each support column comprises a heater disposed on or in the associated support column;
a powder deposition system configured to deposit a powder layer along an upper surface of the build plate, wherein the powder deposition system is vertically displaceable relative to the build plate;
an optics assembly configured to direct laser energy from one or more laser energy sources towards the build plate, wherein exposure of the powder layer to the laser energy melts at least a portion of the powder layer;
a build plate sensor configured to sense an orientation of the build plate; and
at least one processor operatively coupled to each heater and to the build plate sensor, the at least one processor configured to adjust a length of each support column based at least in part on the sensed orientation of the build plate by independently setting a temperature set point for each heater to adjust a temperature profile along each support column.
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This application claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 62/741,836, entitled “ADDITIVE MANUFACTURING SYSTEM WITH FIXED BUILD PLATE”, filed on Oct. 5, 2018, which is herein incorporated by reference in its entirety.
Disclosed embodiments are related to systems for additive manufacturing.
In a selective laser melting or metal powder bed fusion processes, one or more incident laser beams are scanned over a build surface that consists of a thin layers of metal powder deposited on a build plate. At the point of irradiation of each laser beam, if the energy of each point is sufficient, the metal powder is heated to the point where the individual powder particles melt and form a molten pool. As each laser point is scanned over a shape on the build surface, the resulting melt pools and melt tracks solidify into a solid metal structure of a desired shape corresponding to the scanned pattern. Once one layer is complete, the build plate on which the powder bed is deposited is typically indexed downwardly and a new layer of fresh metal powder is spread over the build surface. If a melt track on a subsequent surface is scanned over a track a track from the previous scan, the layers are fused together by the melt pool. In this manner, a three-dimensional part can be produced by processing multiple sequential layers.
Both single laser and multi-laser systems are used. Some systems use a pair of galvanometer mounted mirrors to scan each laser beam over the desired pattern on the build surface. Some systems use motion stages to scan the laser over the build surface. Some systems use a combination of motion stages and galvanometers to scan the laser over the build surface. Systems that use galvanometers as part of the scanning method often use f-theta or telecentric lens to help keep the incident angle of the laser beam onto the build surface as close to perpendicular as possible for a given build surface size. The spacing between the final optical component of any laser path (e.g., final optics, galvanometer, mirror, telecentric lens or f-theta lens) may be on the order of a few millimeters up to a hundred or more centimeters.
In one embodiment, an additive manufacturing system comprises a build plate and a shroud vertically displaceable relative to the build plate. The shroud defines a boundary around a build volume above the build plate. The system further comprises a powder deposition system configured to deposit a powder layer along an upper surface of the build volume, and the powder deposition is vertically displaceable relative to the build plate. The system also comprises an optics assembly configured to direct laser energy from one or more laser energy sources towards the build volume. Exposure of the powder layer to the laser energy melts at least a portion of the powder layer.
In another embodiment, a system for leveling a build surface of an additive manufacturing system a build plate, a base, and a support column extending between the base and the build plate and configured to support at least a portion of a load applied to the build plate. A heater is attached to the support column and configured to heat a portion of the support column.
It should be appreciated that the foregoing concepts, and additional concepts discussed below, may be arranged in any suitable combination, as the present disclosure is not limited in this respect. Further, other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments when considered in conjunction with the accompanying figures.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
The inventors have recognized and appreciated that numerous advantages associated with additive manufacturing systems such as selective laser melting or other powder bed fusion systems that allow for precise control over the position of a build surface during a build process. In conventional systems, a build plate surrounded by a fixed powder containment shroud is translated downwardly between processing steps by a step distance corresponding to a thickness of powder layer used for each processing step. For example, typical step distances range from about 20 μm to about 150 μm based on the powder thickness and layer resolution required for a particular additive manufacturing process. However, the inventors have appreciated that this conventional approach involving moving the build surface between each processing step may not be scalable to systems configured to manufacture larger printed parts due to the increased mass of a completed build associated with increased size of an additive manufacturing machine's print volumes. For instance, in a system configured for manufacturing a steel or stainless part in a 500 mm×500 mm×500 mm print volume, the mass of the print volume may be upwards of 1000 kg at the end of the build process. As another example, a system with a build volume of 1 cubic meter, the print volume mass may be 8000 kg or more. The inventors have recognized that conventional arrangements for controlling the build surface during a build process (e.g., arrangements to index a build plate downwardly between successive processing steps) may not be capable of precisely and accurately moving such large masses by the required step distances. For example, conventional actuator systems for controlling a build surface may not be capable of accommodating the wide range of print volume mass (e.g., 0 kg up to thousands of kg) exerted on the build surface throughout an additive manufacturing process while maintaining an accurate layer thickness on the micron scale for each processing step.
In view of the foregoing, the inventors have appreciated numerous advantages associated with additive manufacturing systems utilizing a fixed build plate in which the other components, such as a powder deposition system (e.g., a powder recoater arrangement), optics unit, and powder containment shroud are arranged to index upwardly relative to the fixed build surface during a build process. For example, such systems may allow for the use of robust support structures for the build plate to support the large range of masses throughout a build process. Moreover, the mass of the movable components may be substantially constant throughout a manufacturing process, which may allow for more accurate and/or precise control of the layer thickness throughout the build process.
In one embodiment, an additive manufacturing system includes a build plate, which may be substantially fixed in place throughout a build process. For example, the build plate may be constructed to define a stationary bottom support surface of a build volume that extends above the build plate. In this manner, the build plate does not index upwardly or downwardly between successive steps of the build process. However, it should be understood that a fixed build plate may undergo some movement during a build process, such as to adjust an orientation of the build plate to maintain the build plate level throughout the build process, as described in more detail below. A shroud is vertically displaceable relative to the build plate to define a boundary around the build volume. For example, the shroud may extend vertically during each step of the build process by a distance corresponding to the powder layer thickness such that the build volume increases throughout the build process. As described in more detail below, the shroud is constructed and arranged to contain a volume of powder and/or portions of a manufactured part within the build volume throughout the build process. A powder deposition system, such as a recoater system or other suitable construction, may be configured to deposit layers of powder along an upper surface of the build volume, and the powder deposition system is vertically displaceable relative to the build plate. The system further includes an optics assembly configured to direct laser energy from one or more laser energy sources towards the build volume. Exposure of the uppermost powder layer in the build volume to the laser energy melts at least a portion of the powder layer (e.g., according to a desired two-dimensional pattern). During the build process sequential layers of a manufactured part may be formed by indexing the shroud and powder deposition system upwardly relative to the fixed build plate by a distance corresponding to the powder layer thickness, and fusing a portion of each sequential layer as desired. In some embodiments, the optics assembly also may be vertically displaceable relative to the build surface, and may be indexed upwardly along with the shroud and powder deposition system between processing steps. In other embodiments, a focal length of the optics unit may be adjusted using optical components while its mechanical mounting remains fixed. Either construction may allow the focal point of the optics assembly to adjust vertically as the build volume extends upwardly above the build plate. In this manner, a three-dimensional part may be built up layer-by-layer from the fixed build plate.
In addition to the above, the inventors have appreciated that a build surface in an additive manufacturing system must be maintained substantially flat and level compared to both an optics unit and a recoater system (or other suitable powder deposition system) throughout a build process. For example, if the build surface is not level to the optics unit, the focal point of the laser(s) may not coincide with the build surface across the entire build surface. Processed powder in the areas that are out of focus of the lasers may not melt properly, which may result in poor mechanical properties of a manufactured part. If the build surface is not level to the recoater system, the powder layers that are processed on the build surface may have variable thickness, which may impact the ability of the layer to be melted during a processing step. For example, if a thickness of some areas of a layer is too large, those areas may not fully melt when scanned with the lasers. This incomplete melting will result in a weak or nonexistent mechanical connection between the processed layer and the build plate (in the case of the first layer deposited on the build plate) or between the processed layer and subsequent layers. Such weak connections can be detrimental for multiple reasons. For example, in the case of the first layer, the weak connections may cause the part to delaminate from the build plate during the build process, which can cause the part to peel away from the build plate and contact the recoater blade during subsequent recoating steps, leading to a failure of the build process. Moreover, weak connections between processed layers may lead to discontinuities within a manufactured part, which can adversely affect the mechanical robustness of the part, and/or lead to failure of the build process.
However, the inventors have appreciated that leveling of the build surface also becomes difficult as the build volume and mass are increased. For example, while multiple actuators mounted under the build plate might be used to adjust the level of the build plate, such arrangements may be undesirable in that they add cost, mechanical complexity and control challenges related to achieving the positioning requirements for the build plate. In some instances, the build plate might be manually shimmed to flat and level, but such an approach would require significant time and effort and can be very difficult and/or dangerous as the build volumes are increased and/or when using a heated build plate, as discussed below. Leveling the build plate at room temperature may be easier, but plate level may be affected when it is heated up to operating temperature. Also, manual shimming requires operator intervention at the build volume level, which may be undesirable in larger machines. For example, most laser based 3D metal printing systems require an inert atmosphere. If operator intervention is required at the build volume level to mount and shim the build plate for each step of a build sequence, the machine volume has to be purged with inert gas (typically Nitrogen or Argon) after the operator intervention and before processing. This purging can be slow and expensive.
According to some aspects, the systems described herein may facilitate automated leveling of a build plate throughout a build process while providing support for a large build volume. For example, and as described in more detail below, in some embodiments, such automated leveling may be achieved via controlled thermal expansion of one or more support columns underlying a fixed build plate. Consequently, the systems described herein may avoid one or more of the above-noted deficiencies of conventional approaches for leveling a build surface.
In addition to the above, the inventors have recognized that heating of a build plate may be advantageous in some instances. For example, as the temperature of the build plate is increased, the induced thermal stress on a manufactured part may be reduced. Also, with some materials, maintaining the build volume above a minimum temperature may aid in improving one or more properties of the manufactured part, such as one or more metallurgical properties. In some instances, build plate operating temperatures ranging from about 150° C. to about 500° C. may be suitable. However, the inventors have also recognized that build plate heating may adversely affect the leveling, flatness, and/or positioning tolerance of a build surface, and that excess heat from the build plate must be contained to prevent thermal conduction from causing undesired heating in other components of the additive manufacturing system.
In view of the above, some aspects described herein may allow for heating of a build plate to a desired temperature while providing required support and/or leveling of the build plate. For example, in some embodiments, a build plate of an additive manufacturing system may be mounted on a fixed plate including a heater. Conduction may cause the temperature of the build plate to track a set temperature of the heated fixed plate. In some embodiments, the fixed plate may be mounted on one or more support columns that carry the mechanical load from the fixed base to a base of the additive manufacturing system. As described in more detail below, a temperature profile along each of the support columns may be individually adjusted, and the resulting thermal expansion and induced thermal stresses in the support columns may be used to level the fixed based and the build surface throughout a build process. Moreover, in some embodiments, a heated fixed base may not be included, as the current disclosure is not limited in this regard. For example, the support columns may be attached directly to the build plate, and the temperature profile along the support columns may be used to bring the build plate to a desired temperature, in addition to facilitating leveling of the build plate.
In one exemplary embodiment, an additive manufacturing system includes a fixed base on which a build plate is mounted. This fixed base is attached to a machine base (i.e., a base or outer casing of the additive manufacturing system) through a set of support structures, such as support columns. A powder containment shroud surrounds the build plate and the fixed base and is vertically displaceable relative to the build and fixed plates. The shroud is supported by actuators such as vertical motion stages that allow the shroud to be vertically displaced relative to the build plate. A recoater system is supported above the build plate and can be vertically displaced relative to the build plate via another set of actuators or motion stages coupled to the recoater system. An optics assembly is mounted over the build plate. Depending on the embodiment, the optics assembly may comprise a galvanometer system that scans laser beams over the build surface, a fixed optics unit mounted on a gantry system that allows the optics unit to be mechanically scanned in a plane over the build surface, and/or a combination of galvanometer system mounted on a moving gantry system. In the case of a fixed optical focal length, the optics unit (galvanometer or gantry system) may be coupled with a vertical motion system that allows the unit to be vertically displaceable relative to the build plate. If the optics unit has a variable focal length from internal optical components, then the optics unit may remain in a fixed vertical position that is sufficiently high such that it doesn't interfere with the highest possible build surface or upper positions of the recoater and shroud system. A combination of adjustable focal length and adjustable optics unit vertical position can also be used in some embodiments, as the current disclosure is not limited in this regard.
Turning to the figures, specific non-limiting embodiments are described in further detail. It should be understood that the various systems, components, features, and methods described relative to these embodiments may be used either individually and/or in any desired combination as the disclosure is not limited to only the specific embodiments described herein.
In some embodiments, one or more seals may be provided between the build plate 1 and shroud 5 to prevent powder from sifting out of the build volume. For example, the seals may be formed of felt, polymer, rubber, fiber or metallic materials and the seal may be rated to the maximum working temperature of the build and fixed plates. However, it should be understood that a seal may not be included in some embodiments, as the current disclosure is not limited in this regard. For example, contact between the shroud and the perimeter of the build plate may be sufficient to prevent powder from leaving the build volume during the build process. In other embodiments, the shroud may have an extendable construction. For example, a base of an extendable shroud may be attached around a perimeter of the build plate to form a seal that prevents powder from leaving the build volume, and a top of the extendable shroud may be attached to the vertical motion stages to extend the shroud throughout the build process. Accordingly, it should be understood that the current disclosure is not limited to any particular shroud construction or sealing arrangement to contain powder within the build volume during a build process.
As noted above, the support structure for the fixed plate and/or build plate can be used to level the fixed plate and build plate relative to the machine base and other components mounted to the machine base throughout the build process. One exemplary embodiment of such a system is described in more detail in connection with
If the system shown in
Accordingly, some embodiments may be configured to provide a more controlled thermal state relative to the embodiment shown in
Once the system has reached thermal equilibrium, the surface of the build plate can be measured for level. For example, these level measurements can be obtained using a distance sensor mounted on the optics unit and by taking multiple measurement over the top surface of the build plate before the first layer of powder is deposited by a recoater system or other suitable powder deposition system. Depending on the embodiment the distance sensor can be optical, mechanical and/or electrical and can provide micron level measurements of the build plate surface position compared to the optics unit or other suitable component of the system. While a distance sensor is described above, it should be understood that the current disclosure is not limited to any particular type of sensor 404, see
Measurements from a distance sensor or other suitable sensor may be used to adjust the temperatures of the heaters mounted on the support columns. In particular, the change in the temperature profile along each support column will result in a net thermal expansion for each support column, and a thermal expansion for a particular temperature profile along the length of a support column may be approximated as described below in connection with
The analysis discussed above in connection with
The change in length due to thermal expansion from case C to case D, δCD, is dependent on the ΔT as well as the geometry factors H, K, L and M. In one example using a 304 stainless steel support column with H=200 mm, K=100 mm, L=50 mm, T1 of 25° C. and T2 of 200° C., T3 would be 134° C. and a ΔT of 10° C. would yield a δCD of 31 μm. This corresponds to a sensitivity of 3.1 μm/° C. This sensitivity can be adjusted even further by adjusting the geometry factors (position of the heater and length of heater) and by changing the support column material to obtain different coefficients of thermal expansion.
It should be understood that the current disclosure is not limited to approximating the net thermal expansion for a particular temperature profile using the above-described model and/or equations. For example, in some instances, the temperature profile along each column may be determined based on all boundary conditions acting on the support columns. Due to the large number of factors that may go into such a calculation, a finite element analysis may be advantageous in providing accurate solution
In addition to being able to level two sides of a flat plate, an array of support columns can be used to level build plates across multiple directions of a build plate, such as along width and length dimensions.
As described above, in some embodiments, one or more support columns may be installed between the fixed plate and the machine base. In other embodiments, one or more support columns may be installed between the fixed plate and an intermediate plate and a secondary set of support columns may be installed between the intermediate plate and the machine base. For example, a build plate that is used in a system with a tall build volume (i.e., a large powder bed build height), the build plate may need to be installed sufficiently high above the machine base such that a full height powder containment shroud can be lowered around the build and fixed plates without contacting the machine base. If this entire height has to be carried by support columns between the fixed plate and machine base, then the support columns may become long enough that designing around buckling load limitations becomes difficult. In this case an intermediate plate configuration may be advantageous.
In some applications, heated support columns can also be used to compensate for variable loads on the build plate. As the build volume increases with each printed layer, the mass of the accumulated powder and printed parts may eventually start to cause a common compression of all support columns as well as in secondary support columns if they are present in the system. This compression may cause an accumulated height error in a printed part over many layers. This compression can be calculated and compensated for by adding a common thermal offset to all support columns at the same time. For example, in on embodiment, adding 1° C. to all heater support columns per 100 printed layers may be suitable to compensate for this type of variable load.
It should be understood that the heaters described herein may be controlled in any suitable manner. For example, in some embodiments, the various heaters may be operatively coupled to a controller 400, see
Further, it should be appreciated that a controller may be embodied in any of a number of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer. Additionally, a controller may be embedded in a device not generally regarded as a computer but with suitable processing capabilities, including a Personal Digital Assistant (PDA), a smart phone or any other suitable portable or fixed electronic device.
Also, a controller may have one or more input and output devices. These devices can be used, among other things, to present a user interface. Examples of output devices that can be used to provide a user interface include printers or display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that can be used for a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a controller may receive input information through speech recognition or in other audible format.
Such controllers may be interconnected by one or more networks in any suitable form, including as a local area network or a wide area network, such as an enterprise network or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks.
Also, the various methods or processes outlined herein may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.
In this respect, the embodiments described herein may be embodied as a computer readable storage medium (or multiple computer readable media) (e.g., a computer memory, one or more floppy discs, compact discs (CD), optical discs, digital video disks (DVD), magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments discussed above. As is apparent from the foregoing examples, a computer readable storage medium may retain information for a sufficient time to provide computer-executable instructions in a non-transitory form. Such a computer readable storage medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present disclosure as discussed above. As used herein, the term “computer-readable storage medium” encompasses only a non-transitory computer-readable medium that can be considered to be a manufacture (i.e., article of manufacture) or a machine. Alternatively or additionally, the disclosure may be embodied as a computer readable medium other than a computer-readable storage medium, such as a propagating signal.
The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a controller, computer or other processor to implement various aspects of the present disclosure as discussed above. Additionally, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that when executed perform methods of the present disclosure need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present disclosure.
Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.
Also, data structures may be stored in computer-readable media in any suitable form. For simplicity of illustration, data structures may be shown to have fields that are related through location in the data structure. Such relationships may likewise be achieved by assigning storage for the fields with locations in a computer-readable medium that conveys relationship between the fields. However, any suitable mechanism may be used to establish a relationship between information in fields of a data structure, including through the use of pointers, tags or other mechanisms that establish relationship between data elements.
Various aspects of the present disclosure may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. Accordingly, while the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art. Accordingly, the foregoing description and drawings are by way of example only.
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